ceph/src/rocksdb/examples/optimistic_transaction_example.cc

   1 // Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #ifndef ROCKSDB_LITE
   7
   8 #include "rocksdb/db.h"
   9 #include "rocksdb/options.h"
  10 #include "rocksdb/slice.h"
  11 #include "rocksdb/utilities/transaction.h"
  12 #include "rocksdb/utilities/optimistic_transaction_db.h"
  13
  14 using namespace rocksdb;
  15
  16 std::string kDBPath = "/tmp/rocksdb_transaction_example";
  17
  18 int main() {
  19   // open DB
  20   Options options;
  21   options.create_if_missing = true;
  22   DB* db;
  23   OptimisticTransactionDB* txn_db;
  24
  25   Status s = OptimisticTransactionDB::Open(options, kDBPath, &txn_db);
  26   assert(s.ok());
  27   db = txn_db->GetBaseDB();
  28
  29   WriteOptions write_options;
  30   ReadOptions read_options;
  31   OptimisticTransactionOptions txn_options;
  32   std::string value;
  33
  34   ////////////////////////////////////////////////////////
  35   //
  36   // Simple OptimisticTransaction Example ("Read Committed")
  37   //
  38   ////////////////////////////////////////////////////////
  39
  40   // Start a transaction
  41   Transaction* txn = txn_db->BeginTransaction(write_options);
  42   assert(txn);
  43
  44   // Read a key in this transaction
  45   s = txn->Get(read_options, "abc", &value);
  46   assert(s.IsNotFound());
  47
  48   // Write a key in this transaction
  49   txn->Put("abc", "def");
  50
  51   // Read a key OUTSIDE this transaction. Does not affect txn.
  52   s = db->Get(read_options, "abc", &value);
  53
  54   // Write a key OUTSIDE of this transaction.
  55   // Does not affect txn since this is an unrelated key.  If we wrote key 'abc'
  56   // here, the transaction would fail to commit.
  57   s = db->Put(write_options, "xyz", "zzz");
  58
  59   // Commit transaction
  60   s = txn->Commit();
  61   assert(s.ok());
  62   delete txn;
  63
  64   ////////////////////////////////////////////////////////
  65   //
  66   // "Repeatable Read" (Snapshot Isolation) Example
  67   //   -- Using a single Snapshot
  68   //
  69   ////////////////////////////////////////////////////////
  70
  71   // Set a snapshot at start of transaction by setting set_snapshot=true
  72   txn_options.set_snapshot = true;
  73   txn = txn_db->BeginTransaction(write_options, txn_options);
  74
  75   const Snapshot* snapshot = txn->GetSnapshot();
  76
  77   // Write a key OUTSIDE of transaction
  78   db->Put(write_options, "abc", "xyz");
  79
  80   // Read a key using the snapshot
  81   read_options.snapshot = snapshot;
  82   s = txn->GetForUpdate(read_options, "abc", &value);
  83   assert(value == "def");
  84
  85   // Attempt to commit transaction
  86   s = txn->Commit();
  87
  88   // Transaction could not commit since the write outside of the txn conflicted
  89   // with the read!
  90   assert(s.IsBusy());
  91
  92   delete txn;
  93   // Clear snapshot from read options since it is no longer valid
  94   read_options.snapshot = nullptr;
  95   snapshot = nullptr;
  96
  97   ////////////////////////////////////////////////////////
  98   //
  99   // "Read Committed" (Monotonic Atomic Views) Example
 100   //   --Using multiple Snapshots
 101   //
 102   ////////////////////////////////////////////////////////
 103
 104   // In this example, we set the snapshot multiple times.  This is probably
 105   // only necessary if you have very strict isolation requirements to
 106   // implement.
 107
 108   // Set a snapshot at start of transaction
 109   txn_options.set_snapshot = true;
 110   txn = txn_db->BeginTransaction(write_options, txn_options);
 111
 112   // Do some reads and writes to key "x"
 113   read_options.snapshot = db->GetSnapshot();
 114   s = txn->Get(read_options, "x", &value);
 115   txn->Put("x", "x");
 116
 117   // Do a write outside of the transaction to key "y"
 118   s = db->Put(write_options, "y", "y");
 119
 120   // Set a new snapshot in the transaction
 121   txn->SetSnapshot();
 122   read_options.snapshot = db->GetSnapshot();
 123
 124   // Do some reads and writes to key "y"
 125   s = txn->GetForUpdate(read_options, "y", &value);
 126   txn->Put("y", "y");
 127
 128   // Commit.  Since the snapshot was advanced, the write done outside of the
 129   // transaction does not prevent this transaction from Committing.
 130   s = txn->Commit();
 131   assert(s.ok());
 132   delete txn;
 133   // Clear snapshot from read options since it is no longer valid
 134   read_options.snapshot = nullptr;
 135
 136   // Cleanup
 137   delete txn_db;
 138   DestroyDB(kDBPath, options);
 139   return 0;
 140 }
 141
 142 #endif  // ROCKSDB_LITE